Age-hardening austenitic stainless steel



Jan. 4, 1955 p. A. JENNINGS AGE-HARDENING AUSTENITIC STAINLESS STEELFiled Dec. 31, 1952 Carbon 0.08% to /.502, Chromium I22 la 30% Manganese7x to 20% Nitrogen 0. I96 fa 0.60%

Silicon pr: nof owr 0.45%, Iron remainder INVENTOR PAUL A. JENNINGS %L,L ,4 ATTORNEY United States Patent AGE-HARDENING AUSTENITIC STAINLESSSTEEL Paul A. Jennings, Baltimore, Md., assignor to Armco SteelCorporation, a corporation of Ohio Application December 31, 1952, SerialNo. 328,882

7 Claims. (Cl. 75-426) My application is a continuation in part of mycopending application Serial No. 207,591, filed January 24, 1951', andentitled High Temperature Steel and Articles, now abandoned whichapplication is a continuationqnpart of my U. S. Letters Patent 2,602,738which issued on an application filed January 30 1950, as acontinuationin-part of my then ctr-pending application, Serial No.19,480, filed April 7, 1948, now Patent 2,495,731 of January 31, 1950',which is a continuation-in-part of my then co-pending application SerialNo. 786,976, filed November 19, 1947, now abandoned, which in turn is acontinuation-in-part of my application, Serial No. 762,863, filed July23, 1.947, also abandoned, and the invention relates to high temperaturestainless steel, especially to articles in the form of valves, valveparts and other internal combustion engine components intended for useWhile hot in corrosive atmospheres.

Among the objects of my invention is the provision of strong, tough anddurable stainless steel, and various internal combustion engine valves,and engine components fashioned of the same for elevated temperatureuse, which steel products function in a highly satisfactory manner insuch fields as passenger car, truck, aircraft, diesel and marine vesselengine use, and which offer great hardness at the high temperatures.encountered in such use and substantial resistance, in the heatedcondition, to hot corrosive atmospheres such as those containing thecombustion products of anti-knock gasolines illustratively of thetetra-ethyl lead and lead bromide varieties.

Other objects of my invention in part will be obvious and in partpointed out more fully hereinafter.

The invention accordingly consists in the combination of elements,composition of materials and in the several products as describedherein, the scope of the application of which is indicated in thefollowing claims.

The single figure of the accompanying drawing represents a specificproduct and steel composition thereof falling Within the scope of myinvention.

As conductive to a clearer understanding of certain features of myinvention, it may be noted at this point that a great variety ofheretofore known valves and valve parts intended for use as operatingcomponents of internal combustion engines or the like have becomeobsolete for such reasons as increased engine temperatures incident togreater engine power and speed. In average passenger cars, for example,the temperatures encountered by the valves frequently are as high as 700degrees F. or more at the fuel intake position, and as high as 1100degrees to 1450 degrees F. or more at the exhaust position. Thesetemperatures ordinarily are even higher in truck, bus, marine vessel, oraircraft engines, especially in the region where the exhaust valvesoperate.

Low-alloy steel valves, for example, which formerly operatedsatisfactorily in internal combustion engines now are found in mostinstances to be unacceptable, and particularly so on the exhaust side ofthese engines. The valves usually burn or warp very quickly at the highoperating, temperatures, thus impairing engine efficiency and requiringfrequent replacement. While hot, the working parts commonly developoxide scale which detrimentally affects proper seating. In turn, failureof the valve to seat properly allows leakage or blow-by of the hotgases, thus increasing the valve temperature and burning away the metal.An example of this type valve is one containing about 0.45% carbon,8.50% chromium, 3.25% silicon, and the remainder substantially all iron.

they enjoy adequate scaling resistance.

of relatively high-alloy steel valves and parts likewise suffer greatdetriment and rapid deterioration when exposed to the fuel combustionproducts.

A number of stainless steel valves, and valves made of other high-alloymetal, for example, have been introduced for better serving present-dayneeds. Some of these are of ferritic grade steel. Others aremartensitic. In some, there is a high-silicon content and, as a result,Unfortunately, however, they have poor resistance to lead compounds andare decidedly inferior in matters of hot-hardness and stretch resistanceunder certain operating conditions.

There are still other valves in the prior art, these being of austeniticchromium-nickel stainless steel grade. The amounts of silicon in theconventional austenitic steel products range from about 0.50% to 4.0% ormore. In general, the austenitic steel valves have a more favorablelattice structure for resisting stress-rupture and creep at elevatedtemperatures than do the ferritic or martensitic products. It is alsotrue that the relatively high-alloy content of the chromium-nickelaustenitic steel favors resistance to scaling from heat at enginetemperatures. A further advantage often arising from austenitic steelvalve products is their freedom from phase transformation and, in thisrespect, freedom from volume changes and any resulting tendencies suchas warping, sticking or cracking during the heating and cooling cyclesbrought about by the heat engine and its operation. The many valves ofthis character in the prior art, however, leave much to be desired or"resistance to corrosive attack by hot lead compounds.

An outstanding object of my invention, accordingly, is the provision ofa high temperature heat-resistant, corrosion-resistant stainless steeland various valves, valve parts and internal combustion enginecomponents fash ioned of the same having substantial strength at thetemperatures of use, which are substantially free of phasetransformation, are hot hard, resist stretch, and efliciently andreliably resist oxidation in the presence of heat and leaded fuelcombustion products.

Referring now more particularly to the practice of my invention, 1provide low-silicon, high-nitrogen austenitic chromium-manganesestainless steel internal combustion engine valves, valve parts, andvarious other internal combustion engine components made of the steel,illustratively valves, stems, heads, springs, casings, claddings,linings or surfacings. In preferred composition, my products includeabout 0.08% to 1.50% carbon, from 12% to 30% chromium, less than about2% nickel, amounts of manganese ranging from 5% to 20%, with the siliconcontent not exceeding 0.45%, with nitrogen from 0.06% to 0.60%, andtheremainder substantially all non. Moreover, the sum of the nitrogenand carbon contents amounts to at least 0.40%. And the relative amountsof carbon, chromium, nickel, manganese and nitrogen are such as to yielda substantially fully austenitic structure.

Preferably, for desired hardness at the high temperatures encountered inactual use, the carbon content amounts to some 0.40% to 1.50% and thenitrogen from 0.20% to 0.55%.

By maintaining a substantial manganese content and the silicon contentbelow about the 0.25% figure, I find sharp improvement in resistance ofthe steel products to corrosion and attack by products by combustionresulting from the burning of leaded fuel. At about 0.15% silicon and ondown to 0.10% or less, this improvement is even more pronounced, and thehot-hardness is not adversely affected. Both the hot-hardness andcorrosion-resistance are even more favorable where the carbon exceedsabout 0.40% and the silicon ranges from about 0.15% on downsubstantially to zero in amount. The smaller quantities of siliconaccordingly are usually preferred.

Patented Jan. 4, I955 The inclusion of manganese results from mydiscovery that nickel in steels of the stainless grade often has anadverse effect upon the corrosion resistance of valve products while thelatter operate in the presence of hot lead compounds. By supplanting thenickel ordinarily required for providing a steel of austenitic qualitywith manganese an austenitic balance steel is had and the adverse effectof nickel upon corrosion resistance in the combustion products of leadedfuels is importantly dispelled. Moreover, it seems that the steel ofhigh manganese content has a greater solubility for carbon and as suchpermits greater hot hardness as higher temperatures are achieved.Additionally it has a much greater solubility for nitrogen.

In my steel I use the element nitrogen in amounts from 0.06% up to about0.30% or 0.40%, or even up to about 0.60%, as a substitute for anequivalent amount of nickel in the steel, in which event the carboncontent may be as low as 0.08%. tion of increasing the hot-hardness ofthe steel. And as previously noted it also serves as a partialsubstitute for other austenite-forming elements to maintain theaustenitic balance.

There are occasions where my stainless steel products include in thealloy composition thereof, as for special purposes, one or more suchelements as molybdenum, titanium, columbium, tungsten, vanadium, copper,cobalt, tantalum, aluminum, Zirconium, or the like, ranging from quitesmall amounts to substantial amounts not inconsistent with propertiesdesired.

The stainless steel valves, valve parts and engine components which Iprovide have a sulphur content which may be some quantity below about0.04%, or even as much as 0.2% or more. The larger quantities ofsulphur, and especially those between about 0.15% to 0.20%, contributeto the effect of the low-silicon content in promoting resistance toattack by the combustion products of leaded gasolines and the like. Thelarger quantities of sulphur, say those beyond about 0.04%, andespecially from 0.04% to 0.15%, usually improve the machining propertiesof the steel. Amounts of sulphur much beyond 0.20% often introduce hotworking difficulties with certain of the austenitic steels which Iemploy; also, the rate of improvement of resistance to lead oxidecorrosion usually decreases for these greater amounts. The phosphoruscontent of my products preferably is below about 0.04%.

The particular amounts of such elements as chromium, manganese andnitrogen present in the internal combustion engine products which Iprovide assure excellent heat resistance and resistance to oxidation atthe high temperatures encountered. Also, the inclusion of nitrogen andthe restriction of silicon to the critically small amounts indicated,contribute to corrosion-resistance of the products, in the combustionproducts of leaded fuels, as where the steel takes the form of anexhaust valve or part exposed to aircraft, truck or passenger car engineexhaust gases. By virtue of the austenitic quality of the steel, myvalve products suffer substantially no phase transformation duringheating and cooling cycles and, accordingly, are free of volume changesand difiiculties often following upon change of phase. The valves arestrong, tough and hot hard at the high temperatures encountered. Theyresist scaling, warping and cracking at full temperature and upon beingcooled and reheated.

The effect of the nitrogen addition upon hot-hardness is demonstrated bythe comparative figures given in Table I below. The samples analyzeapproximately 21% chromium, 9% manganese, nickel up to about 2%, 0.10%silicon, .50% carbon, with varying nitrogen contents and remainder iron.All samples were heated at about 2150 degrees F. for one hour, thenwater-quenched, and finally aged at a temperature of about 1350 degreesF. to 1400 degrees F. The hot-hardness tests were made with a cold ballpenetrator at 1400 degrees F. and are reported in Brinell numbers. Thecorrosion tests were made by immersing the samples in molten leadoxy-bromide contained in a new magnesia crucible at a temperature of1550 degrees F. for one hour, the weight loss being reported in gramsper square decimeter.

The nitrogen serves the funcill) 4 TABLE I Influence of nitrogen onhot-hardness and resistance to lead oxy-bromide of chromium-manganesestainless steel Hot Sample 0 Mn Gr 51 Ni N hardness, gg

In Table I it is noted that with nitrogen in the amount of 0.30% (sample6374) a hardness of 155 Brinell is had but with 0.40% (sample 6492) thisamounts to 185. Also it is noted that the weight loss in molten leadoxybromide decreases from 10.18 grams per square decimeter per hour to4.59. As a further point it is observed that with an increase in nickelcontent (sample 6389 as compared with 6374) there is a slight loss ofhothardness (152 Brinell as compared with 155) and a substantial loss inresistance to molten lead oxy-bromide (17.60 grams per square decimeterper hour weight loss as compared to 10.18).

The effect of nitrogen as a substitute for nickel is especiallyemphasized by hardness tests taken at various high temperatures andillustrated in Table II given below, where two samples of a 21%chromium, 9% manganese stainless steel are presented, one being of lownitrogen and high nickel content, another of low nickel and highnitrogen content. In both cases the samples were annealed at 2150degrees F. for one hour and then waterquenched followed by aging at 1350degrees F. for nine hours and water-quenched. Here as before, thehothardness tests were taken with a cold ball penetrator and reported inBrinell and as to the corrosion tests were made in molten leadoxy-bromide at 1550 degrees F. for one hour and the weight loss reportedin grams per square decimeter per hour. Additional corrosion tests weremade at a temperature of 1675 degrees in molten lead oxide contained inmagnesia crucible, the weight loss being similarly reported.

TABLE II(a) Influence of nitrogen on hot-hardness at varioustemperatures, analysis of samples Heat l 0 Mn P S S1 C1 Ni N 49309. ...l0. 614 9.34 i 0.02!) 0.008 0.00 21. 43 4.00 0.05 6492 .500 9.20 l .013.015 .08 21.21 .12 .40

TABLE 11(1)) Properties lioom Hot hardness (Brinell) at- I and Lead emp.f. oxide Heat (R00 t i g f" magnesia Well 0) 1.40m F. I 1,500 F. I 1,000F. crucible I 49369 29.7 145 131 l 115 l 15.80 19.45 6492.-" 35.8 171 i101 1 4.59 38.35

From the above it will be seen that the example having a nitrogencontent of 0.40% (sample 6492) is substantrally harder at the respectivetemperatures of 1400 degrees F., 1500 degrees F. and 1600 degrees F.than the example with the low nitrogen content but with a 4.0% nickelcontent (sample 49369). Also it will be seen that there is much lesscorrosive attack by molten lead oxybromide, although somewhat greaterattack by the molten lead oxide.

Certain further benefits are bad by the inclusion in my stainless steelof molybdenum in amounts up to about 9%; generally satisfactory resultsare had with molybdenum amounting to about 2% to 5%. The particularbeneficial effects on hot hardness are illustrated by the results givenin Table III below in which, for a 21% chromium, 9% manganese stainlesssteel with about 0.60% carbon and 0.30% nitrogen, various hardnessfigures are given for samples of differing molybdenum contents. In eachcase the sample was heated to about 2150 degrees F. for one hour, thenwater-quenched and finally aged at a temperature of about 1350 degreesF. to 1400 degrees F. And, as before the hot-hardness tests were madewith a cold ball penetrator at 1400 degrees F. and reported in Brinellnumbers. The corrosion tests likewise were made by immersing the samplesin molten lead oxy-bromide contained in a magnesia crucible at atemperature of 1550 degrees F. for one hour and the weight loss reportedin grams per square decimeter per hour.

TABLE III Hot hardness, 1,400 F.

Lead oxybromide Sample 0 Mn Si N OP-H ocoo mowooo tun-unto Thus it willbe seen that in this invention there is provided a low-siliconhigh-nitrogen austenitic chromiummanganese stainless steel and varioushigh temperature articles and products fashioned of the same, in whichthe various objects noted hereinbefore together with many thoroughlypractical advantages are successfully achieved. It will be seen that theproducts are well suited for resisting corrosion in the presence ofcombustion products of leaded fuels.

While certain of the articles which I provide take the form of internalcombustion engine valves, valve parts and other internal combustionengine components, it will be understood that certain advantages of theinvention are had with other products of the low-silicon steel, amongwhich are high-temperature gas turbine noz zles, turbine parts adjacentto the nozzle, and any of a variety of supercharger components. I

While all the benefits of my invention are en oyed in the steel articlesdescribed above, certain of these benefits, including great hardness athigh temperatures, are enjoyed even where the silicon content of thesteel is not restricted to the maximum figure of 0.45% but is includedin amounts up to 4.0% or even more.

As many possible embodiments may be made of my invention and as manychanges may be made in the embodiment hereinbefore set forth, it will beunderstood that all matter described herein is to be interpreted asillustrative and not as a limitation.

I claim as my invention:

1. Age hardening austenitic stainless steel having a hardness when agedexceeding 145 Brinell at a tempera ture of 1400" F. and containing about0.08% to 1.50% carbon, 12% to 30% chromium, 7% to 20% manganese,

.l% to 0.60% nitrogen, with the sum of the carbon and nitrogen contentsat least 0.40%, and with the various elements all in such proportions asto assure a substantially fully austenitic structure, and the remaindersubstantially all iron.

2. Age-hardening austenitic stainless steel having a hardness when agedexceeding Brinell at a temperature of 1400 F., and containing about0.08% to 1% carbon, 19% to 23% chromium, 7% to 11% manganese, molybdenumup to 9%, .l% to .60% nitrogen, with the sum of the carbon and nitrogencontents at least 0.40%, and the remainder substantially all iron.

3. Age-hardening austenitic stainless steel having a hardness exceeding145 Brinell at a temperature of 1400 degrees F. and substantialresistance to corrosion in the presence of leaded fuel combustionproducts, and contaming about .08 to .7% carbon, 19% to 23% chromium, 7%to 11% manganese, 0.20% to 0.55% nitrogen, incidental amounts of nickel,silicon not exceeding 0.25%, with the sum of the carbon and nitrogencontents at least 0.40%, and the remainder substantially all iron.

4. Age-hardening austenitic stainless steel having a hardness exceeding145 Brinell at a temperature of 1400 degrees F. and substantialresistance to corrosion in the presence of leaded fuel combustionproducts, and containing about .08% to .7% carbon, 19% to 23% chromium,7% to 11% manganese, 2% to 5% molybdenum, .l% to .4% nitrogen, siliconnot exceeding 0.25%, with the sum of the carbon and nitrogen contents atleast 0.40%, and the remainder substantially all iron.

5. Age-hardening austenitic stainless steel having a hardness exceeding145 Brinell at a temperature of 1400 degrees F. and substantialresistance to corrosion in the presence of leaded fuel combustionproducts, and containing about .08% to 1% carbon,-l9% to 23% chromium,7% to 11% manganese, nickel less than 2%, sulphur up to 0.15%,molybdenum up to 9%, .l% to .60% nitrogen, silicon not exceeding 0.45with the sum of the carbon and nitrogen contents at least 0.40%, and theremainder substantially all iron.

6. Age-hardening austenitic stainless steel internal combustion engineexhaust valves comprising approximately .08% to .7% carbon, 19% to 23%chromium, 7% to 11% manganese, .2% to .55 nitrogen, with the sum ofcarbon and nitrogen contents at least about 0.40%, and the remaindersubstantially all iron.

7. Age-hardening austenitic stainless steel internal combustion engineexhaust valves comprising approximately .08% to .7% carbon, 19% to 23%chromium,

. 7% to 11% manganese, .l% to .60% nitrogen, molybdenum up to 5%, nickelless than 2%, sulphur up to 0.15%, silicon not exceeding 0.45%, with thesum of the carbon and nitrogen contents at least about 0.40%, and theremainder substantially all iron.

References Cited in the file of this patent UNITED STATES PATENTS2,212,495 De Vries Aug. 27, 1940 2,380,854 Lorig July 31, 1945 2,496,247Jennings Jan. 31, 1950

1. AGE HARDENING AUSTENITIC STAINLESS STEEL HAVING A HARDNESS WHEN AGEDEXCEEDING 145 BRINELL AT A TEMPERATURE OF 1400*F. AND CONTAINING ABOUT0.08% TO 1.50% CARBON, 12% TO 30% CHROMIUM, 7% TO 20% MANGANESE, .1% TO0.60% NITROGEN, WITH THE SUM OF THE CARBON AND NITROGEN CONTENTS ATLEAST 0.40%, AND WITH THE VARIOUS ELEMENTS ALL IN SUCH PROPORTIONS AS TOASSURE A SUBSTANTIALLY FULLY AUSTENITIC STRUCTURE, AND THE REMAINDERSUBSTANTIALLY ALL IRON.